In gas and petroleum industry, the waste gas stream from the sweetening process of a sour natural gas stream is commonly referred as acid gas. Chemical Looping Combustion (CLC) technology has the potential to exploit the combustible fraction of acid gas, H2S, to produce energy obtaining a flue gas highly concentrated on CO2 and SO2, which can be cost-effectively separated for subsequent applications, such as sulfuric acid production. At the same time, a concentrated CO2 stream ready for storage is obtained. The resistance of oxygen carriers to sulfur becomes crucial when an acid gas is subjected to a CLC process since the H2S content can be very high. In this work, a total of 41 h of continuous operation with acid gas and H2S concentrations up to 20 vol.% has been carried out in a 500 W-th CLC unit with two oxygen carriers based on Cu (Cu14 gamma Al) and Fe (Fe20 gamma A1). The formation of copper sulfides and the SO2 emissions in the air reactor made the Cu14 gamma Al material not adequate for the process. In contrast, excellent results were obtained during acid gas combustion with the Fe20 gamma Al oxygen carrier. H2S was fully burnt to SO(2)in the fuel reactor at all operating conditions, SO2 was never detected in the gas outlet stream of the air reactor, and iron sulfides were never formed even at H2S concentrations as high as 20 vol.%. Furthermore, it was found that a H2S content of 20 vol.% in the acid gas was high enough to turn the CLC process into an auto-thermal process. Based on these results, it can be concluded that the Fe-based materials prepared by impregnation are very adequate to exploit the energy potential of acid gas mixtures with CO2 capture. (C) 2014 Elsevier Ltd. All rights reserved.